Fluoroelastomer compositions are particularly useful as seals, gaskets, and molded parts in systems that are exposed to elevated temperatures and/or corrosive materials. For sealing applications that require resistance to the most extreme conditions, perfluorinated elastomers are used. Such parts are used in applications such as automotive, chemical processing, semiconductor, aerospace, and petroleum industries, among others.
Curable compositions used to make fluoroelastomer compositions often include a fluoropolymer comprising monomer units having a nitrogen-containing cure site to facilitate cure in the presence of a curative. One class of useful cure-site components used in fluoroelastomers includes nitrogen-containing groups such as, for example, nitrites and imidates.
Fluoroelastomer compositions are typically prepared by combining a fluoropolymer resin or gum (sometimes referred to in the art as a fluoroelastomer gum) with one or more curatives to form a curable composition, shaping the curable mixture into a desired shape, and then curing the curable composition until the desired physical properties are achieved. During mixing of the curative(s) and fluoropolymer resin, and in subsequent handling prior to the curing step, the curable mixture may undergo a degree of premature curing (sometimes referred to in the art as incipient curing) that renders the curable composition difficult or impossible to shape. This premature curing is typically accompanied by a viscosity increase, and is referred to in the elastomer curing art as “scorch”. Typically, scorch is reported with reference to “Mooney scorch” which is a measure of the incipient curing characteristics of a rubber compound using the Mooney viscometer. Mooney scorch is typically determined according to a standard test method such as, for example, ASTM D1646-04 “Standard Test Methods for Rubber-Viscosity, Stress Relaxation, and Pre-Vulcanization Characteristics (Mooney Viscometer)”.
In general, the lower the degree of observed scorch, the greater will be the processing window during manufacture of shaped fluoroelastomer articles.